This invention relates generally to printers for use with a web of paper or other sheet material which travels along a fixed linear path. More particularly, the present invention relates to printers of the type where a print device or other drawing instrument is traversed across the width of the web, in a direction perpendicular to the direction of the linear path of the web, to draw figures, characters, and other graphics on the sheet material.
Traditional printers utilizing a traversing head mechanism cause the print head to traverse across the web of paper while moving paper in one of three operational modes: 1) intermittent paper movement; 2) continuous paper movement; or 3) a combination of intermittent paper movement combined with continuous paper movement. In each of these three operational modes to date, the linear paper movement and the traversing movement are monitored independently and utilize electronic means for controlling each of these motions while also providing a means for electronically interlocking the two motions.
In the first mode of operation, the print head accelerates to a printing velocity while traversing across the paper web perpendicular to the length of the web while the paper remains stationary. A position encoder driven by the print head drive motor is used to provide timing information for the incremental placement of the print pattern on the paper. When the print head reaches the end of the printable band, the motor controlling the traversing motion of the print head brings the print head to a controlled stop. While the print head is being stopped, the paper is advanced an amount equal to the vertical height of the printed band. This motion is controlled by an independent motor drive and is monitored by an independent encoder or position transducer which directly or indirectly measures paper movement. When the paper reaches the next print position, the print head motor reverses the traversing direction and then repeats the acceleration, print and deceleration process. This cycle repeats for each required print band. The paper advance motor or an independent paper take-up motor is used to rewind the printed web while a separate means for tension control of the web is provided in most systems.
In the second operational mode, the paper is first placed in motion in one direction prior to or simultaneously with the beginning of the print head traversing cycle. The traversing angle in this case is not horizontal or zero degrees as in the first case, but is determined by the ratio of the linear paper speed and the traversing speed of the print head. This angle is required in order to generate a horizontal print band on the moving paper and is obtained by driving the print head with an x-direction and a y-direction drive mechanism. The traversing motor driving the print head in the x-direction will have the same acceleration, print, deceleration, stop, and reverse characteristics as the first case. Electronic synchronization of the paper feed and the traversing feed (x-direction) motors along with an additional means for controlling and synchronizing the displacement of the print head in the paper direction (y-direction) for creating the required traversing angle is required. At the end of two traversing passes or one complete right and left traversing pass across the web, the y-direction drive mechanism that creates the traversing angle must be reset to it""s original home position to enable the cycle to repeat. This function usually utilizes a separate actuating device and requires high acceleration forces.
The third operational mode uses mode 2 but permits the paper and traversing mechanism to stop at the end of any printed line.
All three of the operational modes described above utilize relatively expensive servo mechanisms for synchronizing two or more axis of motion in order to obtain the required printing precision at high speeds. In addition, as the speed requirement of the printer increases, significantly higher accelerations for starting, stopping, and reversing the traversing motion require even more expensive mechanisms and typically reduce the reliability of the printer due to the increased loads resulting from the high accelerations associated with this type of traversing motion.
Briefly stated, the invention in a preferred form is a printer for printing on a web of material moving continuously in a single direction along a linear path. The printer includes means for advancing the web of material along the linear path and means for printing on the web of material along a print path extending across the linear path. A single motor provides the motive power for advancing the material along the linear path and for reciprocally pushing and pulling the print means between first and second end positions adjacent the opposite first and second sides of the linear path.
The advance means includes a feed drum which is rotatably mounted to the frame of the printer and has an outer surface which frictionally engages and pulls the web material along the linear path. The printer also includes means for tensioning the web of material as it is advanced along the linear path. The tensioning means includes a take-up shaft and means for moveably mounting the take-up shaft to the frame. A leading end of the web of material extending between the take-up shaft and the feed drum is mounted to the take-up shaft such that the web material is wound on the take-up shaft during the printing operation.
The advance means further includes a supply shaft which is mounted to the frame for rotatably mounting a supply roll of web material. The tensioning means further includes a paper tension roller and means for moveably mounting the paper tension roller to the frame. The paper tension roller has an outside surface adapted which engages the web material disposed intermediate the supply shaft and the feed drum.
The means for moveably mounting the take-up shaft and the means for moveably mounting the paper tension roller each include a pair of pendulum arms. Each of the pendulum arms has oppositely disposed first and second end portions, with the first end portion of each pendulum arm being independently pivotally mounted to the frame. The take-up shaft and the paper tension roller are each rotatably mounted to the second end portions of the respective pendulum arms.
The print means includes a pivot beam which extends orthogonally across and adjacent to the linear path of the web. At least one print head is supported on the pivot beam and is moveable along the pivot beam between the first and second end positions. Means are provided for selectively pivoting the pivot beam such that a first end portion of the pivot beam is pivoted in the direction of the linear path when the print head is disposed for moving from the second end position to the first end position and a second end portion of the pivot beam is pivoted in the direction of the linear path when the print head is disposed for moving from the first end position to the second end position.
A drive pulley and an idler pulley are rotatably mounted at the first and second end portions of the pivot beam, respectively, with the output of the motor being coupled to the drive pulley. A drive belt carried on the drive and idler pulleys is driven by the drive pulley in a single direction. The drive belt is linked to the print means for reciprocally pushing and pulling the print head between the first and second end positions.
First and second eccentric cams are rotatably mounted at the first and second end portions of the pivot beam, respectively, and engage with fixedly mounted first and second cam supports, respectively. The first and second eccentric cams each have a cam lobe, with the cam lobe of the second eccentric cam being located 180xc2x0 from the cam lobe of the first eccentric cam. Trip means connected to the drive belt selectively rotates the first and second eccentric cams such that the cam lobe of the first eccentric cam engages the first cam support to pivot the first end portion of the pivot beam in the direction of the linear path when the print head is disposed for moving from the second end position to the first end position and the cam lobe of the second eccentric cam engages the second cam support to pivot the second end portion of the pivot beam in the direction of the linear path when the print head carriage assembly is disposed for moving from the first end position to the second end position.
It is an object of the invention to provide a new and improved printer for printing on a web of continuously moving material.
It is also an object of the invention to provide a printer having a paper advance system which provides a constant tension on the paper web in spite of variations in web tension and thickness.
It is further an object of the invention to provide a printer having horizontal print density and accuracy of the printed horizontal line which is independent of the throughput.
It is also further an object of the invention to provide a printer having a significantly lower power consumption than conventional printers.